The present invention relates to a method of continuous grinding or polishing of web-shaped, textile flat structures.
Grinding or polishing is no longer considered as the best finishing process. In the clothing industry microfilament polyester yarns are used for the warp, and viscous filament or spinning fiber yarns are used for weft on increasing scale. These and other filaments must be polished. After polishing the finest fibrel fibers or microfibers produce new, sport impression. The textiles obtain a soft, flowing impression. It is identified as a "peach skin" effect. Also, during the manufacture of wild leather imitations these effects are desired.
The mechanical equipment for surface changes includes in practice two different types of machines, namely multi-roll polishing machines for polishing the outer surfaces and single roll machines for grinding the outer surfaces. In the multi-roll machines the products in tensioned condition are pulled through four to seven rollers coated with a polishing paper, and the rollers rotate in the running direction of the product or in the opposite direction. The product is brought in friction contact with the polishing surface with a more or less adjustable pressure. The polishing splits the projecting fibers and produces a velvet-like and at a same time very low fibrous pile. Depending on the grain size of the polishing tool, this effect is finer or coarser. Many articles are first polished on relatively coarse polishing rollers and then on fine polishing rollers.
In the microfiber fabrics there is however an opposite row succession. The multiroller machines used in praxis have decisive advantages as compared with the single roller machines, namely: yarn knots can deviate, and, with corresponding adjustment, they are not polished and opened. The polishing rollers are not heated. Therefore the standing time for the polishing paper is longer. The mechanical energy is distributed between the number of polishing locations and therefore reduced. With the use of the single roller machine it is possible to work with an exactly adjustable grinding depth. However, all thickness differences are ground-off. This means that the yarn knots are opened, and the covering selvage and product edges are ground-off and destroyed.
As mentioned hereinabove, the polishing effect is determined first of all by product tensioning, product pressure, polishing grain size and running direction of the polishing roller relative to the product. However, a proper evaluation of these effects is very difficult and their reproducibility is extremely complicated. For example, the condition of the polishing paper is a value which can distort the effects. Also, the faulty adjustments of the product tension can lead to substantial disadvantages. In practice the following approach is taken:
For first pattern adjustment, the individual rollers are decoupled or adjusted to perform free running. Then a user rotates with a finger the respective polishing roller is rotated and simultaneously increases the product wrapping around, or in other words the product coating angle. This is performed while the roller is rotated with forcible pressure. The process must be repeated for each charge since the polishing effect changes due to wear of the polishing device, and moreover even with two identical product qualities some differences can take place, for example, as a result of the expansion and moisture. The above described process is expensive and not economical due to the long stoppage time.
Excessive wrapping increases the removal of the fiber material and reduces the shearing strength. For this process the experience of the grinding machine operator is required. He must select the adjustment in view of the relation between the product tension on the one hand and the wrapping of the polishing roller (product coating angle) on the other hand so as to obtain the best effect with the maximum shearing strength. For this purpose in order to perform the adjustment the machine operator must analyze the value of the ampere-meter on the motor of the polishing roller and the scale value of the guiding roller (product coating angle). As a rule, he adjusts up a pattern recorder. Before and after each grinding passage, a pattern is removed and stored. Therefore, the machine operator must again examine the shearing strength and the product efficiency.
The effect evaluation in many cases is based on observations which, however, have reduced accuracy when the above mentioned disturbances negatively affect the results of the polishing process. The grip of the polishing paper, its wear, the reaction of the product to the adjusted tension, the danger of a fold formation in the longitudinal direction, the expansion conditions of the product, as well as different moisture values and possible electrostatic charges can unfavorably affect the results.